Fig. 2

Tree of life. Schematic presentation of the tree of life. Viruses are depicted as small hexagons. Viral lineages are traced as “lianas” wrapping around the trunk and three major branches - domains of life. Horizontal gene transfer (HGT) between cells and viruses is marked as a source of genetic diversity. Viral origin of eukaryal nucleus and bacterial origin of mitochondria and chloroplasts are depicted. Only chosen phyla are presented on the top of the tree. The taxonomy of Archaea is presented according to Brochier-Armanet et al. [91]. For a more detailed taxonomy of major phyla in Eukarya and Bacteria one may refer to Zhao et al. [92], and Chun et al. [93], respectively